In her first debate as a candidate for U.S. Senate Tuesday night, Harvard law professor Elizabeth Warren declined to criticize her fellow Democratic candidates, taking aim instead at Republican Sen. Scott Brown, whom the Democratic nominee will face, and Wall Street.

"Forbes magazine named Scott Brown Wall Street’s favorite senator. I was thinking that’s probably not an award I’m going to get," she said to applause and laughter from the audience at the University of Massachusetts-Lowell. Two recentpolls put Warren and Brown in a statistical tie.

"America's middle class has been hammered, squeezed and chipped at for a generation now, and it can't take it much longer," she added. "This is what I work on. This is my life's work. I've done research on it, I've written about it, I've advocated for these families. When we hit a financial crisis I went to Washington to try to work on the bank bailout and bring some transparency and accountability to it," she said.

She also made the audience laugh and applaud with the second question, which asked each candidate how they paid for college, since Brown posed nude for Cosmopolitan to pay.

"I kept my clothes on," she quipped. She added that she borrowed money to go to a public university and had a part-time job.

Warren also drew applause for her tough talk on Wall Street. "The people on Wall Street broke this country, and they did it one lousy mortgage at a time. It happened more than three years ago, and there has been no real accountability, and there has been no real effort to fix it. That’s why I want to run for the United States Senate," she said.

When asked how she would react if one of her children joined the military, she said: "This is not a hard question for me. All three of my brothers served in the military and I, in fact, have urged my children, or one of my children, to consider it. He chose not to. But I believe that military service is a real alternative, and it’s an alternative for a career for some, and it’s an important opportunity to be part of America for others, so my answer is, yes, absolutely."

In response to another question on the military, she said all wars should be paid for "in the present time."

"It means either all of go to war, or none of us go to war," she said.

The Boston Herald and the UMass Lowell sponsored the debate, and the moderator was former Democratic House member and current UMass Lowell chairman Marty Meehan. The debate also included state Rep. Tom Conroy, attorney Marisa DeFranco, former Lt. governor nominee Bob Massie, engineer Herb Robinson and City Year co-founder Alan Khazei.

The Democratic candidates generally didn't attack each other, but Khazei seemed to take a shot at Warren toward the end of the debate. "If you think Washington PACs should call the shots, then the Washington establishment will get their way, and this election will be over before it starts," said the Democrat, who lost in the 2009 special election primary to Martha Coakley.

But the debate largely focused on jobs and the economy. "I’ve stood toe-to-toe with the largest financial institutions in the country and sometimes our own government," said Warren. "You have to be willing to take the fight directly to Wall Street and directly to Washington."